Electrophoresis is used for a large number of applications. As an example of but one application, DNA sequencing to determine the genetic composition of a sample of DNA can be undertaken using electrophoresis.
Many existing electrophoresis applications are undertaken using so-called running tanks, in which a sample-containing gel is disposed in an electrophoresis chamber in the tank. Electric current is then applied to the gel by means of an electrode in the tank to cause electrophoresis of the sample.
For safety reasons, the electrophoresis chamber preferably is covered by a lid when energized. To ensure that the lid covers the electrophoresis chamber prior to energizing the gel, interlocks have been provided to break the electric current path between an electrophoresis power supply and the tank electrode when the lid is not properly engaged with the running tank.
As one example of such an interlock, microswitches have been provided on the top edge of running tanks, and the microswitches are closed by a lid when the lid is placed on the tank, thereby completing the electrical circuit between the tank electrode and the power supply. Unfortunately, the tank electrode can be energized anytime the microswitches are depressed, whether by a lid or by a substitute mechanism. Thus, the interlock easily can be defeated.
An alternative interlock is disclosed in U.S. Pat. No. 5,405,520, which discloses a plug that is completely recessed into a running tank cover. The cover is formed with a slot that extends to the plug, and a switch on the running tank is advanced into the slot against the plug when the lid is lowered down onto the tank. When the switch contacts the plug, an electrical circuit is established to the running tank electrode. However, the switch can be "made" by contact with components other than the plug in the cover; consequently, the interlock can be easily defeated.
Still another alternate interlock is exemplified in a device marketed under the trade name "Mupid-21" by Cosmo Bio Ltd. of Japan. In the Mupid-21 device, a running tank cover has a vertical wall and a plug protruding from a front side of the wall. The rear end of the plug is exposed at a rear side of the wall. To engage the lid with a running tank, the lid is lowered onto the tank with the vertical wall of the lid disposed flush against an inside surface of a wall of a power supply bay that is formed as part of the tank. The wall of the power supply bay holds a contact that is connected to the running tank electrode, such that the rear end of the plug wipes the contact when the lid is slid onto the tank. Then, a power supply having a receptacle is advanced into the bay until the plug mates with the receptacle, thereby completing the electrical circuit between the running tank electrode and the power supply.
It happens that a user of an electrophoresis apparatus might undertake many successive electrophoresis experiments over the course of a day, requiring the lid to be removed from the running tank between experiments to modify or replace the gel in the running tank. Unfortunately, the Mupid-21 design necessitates removing the power supply from the bay to remove the lid from the running tank, which users find cumbersome and time consuming. As recognized herein, however, it is possible to provide an electrophoresis running tank assembly which ensures that a power supply cannot be electrically connected to a running tank electrode without first covering the running tank with a lid, and which does not require the power supply to be removed from the assembly to remove the lid from the running tank.
Accordingly, it is an object of the present invention to provide an electrophoresis running tank assembly which prevents energizing a running tank electrode unless a lid is properly positioned on the running tank. Another object of the present invention is to provide an electrophoresis running tank assembly which permits removing the lid from the running tank without removing the power supply from the assembly. Still another object of the present invention is to provide an electrophoresis running tank assembly that is easy to use and cost effective to manufacture.